A mycolyl acetyl trehalose (MAT from Mycobacterium tuberculosis) -endotoxin (ET from the Re mutant of Salmonella typhimurium) mixture in oil droplets was found to be a powerful agent in the regression of transplantable hepatomas of syngeneic guinea pigs. It is our desire to study the factors associated with this biological activity and to find the simplest and most effective combination for the immunotherapy of cancer. The specific objectives of this proposal are as follows: (1) prepare a series of synthetic glycolipids that are structural analogs of MAT, (2) isolate, purify and characterize the lipopolysaccharides from several R-mutants of S. typhimurium in which specific segments of the polysaccharide chain are missing, (3) test various combinations of the synthetic glycolipids and purified ET in oil droplets for tumor regression activity in the guinea pig hepatomas and tumor suppression activity in the L1210 leukemia and solid Lewis lung tumor systems of mice under the condition of low tumor burden, (4) study the nature of interaction of the MAT-ET system at the oil-water interface, and (5) arrive at the simplest glycolipid-ET model system and define the factors required for high biological activity.